In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (see, for example, Non-Patent Literature 1).
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems to LTE have been under study (for example, LTE Advanced (LTE-A)). Accordingly, in the future, it is expected that these multiple mobile communication systems will coexist, and configurations (base station apparatus, mobile terminal apparatus, etc.) that are capable of supporting these multiple systems will become necessary.
In the downlink of the LTE system, the CRS (Common Reference Signal) is defined as a cell-common reference signal. This CRS is used for demodulation of transmission data, measurement of downlink channel quality (CQI: Channel Quality Indicator) for scheduling and adaptive control, and measurement of an average state of the downlink propagation channel for cell search and handover (mobility measurement).
In the meantime, in the downlink of the LTE Advanced (LTE-A) system, study has been made about the CSI-RS (Channel State Information—Reference Signal) defined specially for CQI measurement, in addition to the CRS. The CIS-RS can be used for CQI measurement in plural cells in consideration of transmission/reception of data channel signals by Coordinated Multiple Point (CoMP). The CSI-RS is different from the CRS in that the CSI-RS is used for CQI measurement of adjacent cells while the CRS is used for CQI measurement of a serving cell only.